This invention relates to photosensing devices and to a simplified method of incorporating a III-V negative electron affinity (NEA) photocathode into a photodetector tube structure. A single crystal and substrate, upon which the desired III-V photocathode layers are epitaxially grown, is used directly as the input window of the tube structure.
Negative electron affinity III-V materials comprise a family of new photocathodes with vastly improved performance over conventional S type photocathodes in terms of sensitivity and spectral range. Unlike S cathodes, which are deposited directly on the glass tube faceplate, these new photocathodes are epitaxially grown on relatively thick seed substrates and are independently incorporated into photo-tube structures, either by attaching them directly to the input glass faceplate or by mounting them separately in close proximity to the input faceplate. These types of "mounting" generally result in mechanical complexity and complications due to the specialized clips or holders required. In addition, if the photocathode is not in intimate contact with the window, severe optical problems are generally encountered. One solution to these problems lies in the use of the substrate, upon which the photocathode layers are grown, as the faceplate window of the device.